Search for https://www.ncbi.nlm.nih.gov/nuccore/?term=Ebolavirus%5Borganism%5D+AND+bat on genbank you'll find two batches of bat ebolavirus sequences: one 2019 paper https://pubmed.ncbi.nlm.nih.gov/31002301/ sequencing full Bombali ebolavirus genomes from bats, this study is considered trustful and indicates a bat origin of Bombali. This is also confirmed independently by some Predict sequences such as https://www.ncbi.nlm.nih.gov/nuccore/MT929359.1

And another 2005 paper https://www.nature.com/articles/438575a using nested PCR to obtain short partial Zaire ebolavirus (the genuine Ebola) sequences. This hasn't been replicated since 2005, this paper is not considered trustful.

There is a similar nested PCR story for Reston ebolavirus https://virologyj.biomedcentral.com/articles/10.1186/s12985-015-0331-3 but they didn't bother to upload the sequence to genbank..

Still Marburg (a distant filovirus) also has a clear bat origin.

Together with the serological studies and the lack of other putative reservoir it means that fruit bats are still our best guess.

But the truth is that we don't know for sure.